High mechanical index (HMI) impulses from a diagnostic ultrasound (DUS) transducer in addition to a commercial microbubble infusion can prevent microvascular obstruction and improve functional outcome when used in conjunction with percutaneous coronary intervention (PCI) during acute ST-segment elevation myocardial infarction (STEMI), according to study results published in the Journal of the American College of Cardiology.

Researchers sought to test the safety and efficacy of HMI impulses from a DUS transducer during intravenous microbubble infusion in humans.

Twenty patients with their first STEMI were randomly assigned to receive intermittent HMI impulses with a DUS prior to emergent PCI, and for an additional 30 minutes post-PCI. Another 10 patients were assigned to receive only low mechanical index (LMI) imaging for perfusion assessments before and after PCI. The procedures were conducted during an intravenous perflutren lipid microsphere infusion.


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A control group of 70 patients was selected outside of the time window of ultrasound availability and received only emergent PCI. Researchers then compared initial epicardial recanalization rates prior to emergent PCI and improvements in microvascular flow between the ultrasound-treated groups.

The median door-to-dilation time among patients who received only LMI imaging was 82 ± 26 minutes. Among patients who received HMI impulses, the median time was 72 ± 15 minutes, and the time was 103 ± 42 minutes in the control group.

Researchers observed angiographic recanalization prior to PCI in 60% of patients who received high mechanical index impulses with PCI, compared with 10% who received LMI imaging, and 23% of the control group (P=.002).

No differences were seen in microvascular obstructed segments prior to treatment, although there were significantly smaller proportions of obstructed segments among patients who received high mechanical index impulses at 1 month (P=.001) and improvements in left ventricular ejection fraction (P<.005).

“Early treatment with HMI diagnostic impulses resulted in an improvement in ejection fraction and wall motion scores are 1-month follow-up. This improvement may be related to the long-term effects of restoring microvascular flow early in the treatment period,” the authors wrote.

“By acutely improving microvascular flow in acute STEMI, DUS also may play a critical supplemental role in preventing the remodeling that leads to further reductions in ejection fraction and increased risk for arrhythmic and heart failure complications.”

The authors noted larger trials are needed to assess whether improvements in microvascular outcome with DUS will translate into reduced morbidity and mortality at longer-term follow-up. Future studies should also investigate whether HMI impulses can be employed therapeutically to improve ventricular function and clinical outcomes.

Reference

Mathias W, Tsutsui JM, Tavares BG, et al. Diagnostic ultrasound impulses improve microvascular flow in patients with STEMI receiving intravenous microbubbles. J Am Coll Cardiol. 2016;67(21):2506-2515. doi: 10.1016/j.jacc.2016.03.542.